Conventionally, various techniques for a projector using a prism have been disclosed.
For example, there are provided an optical device, an image modulating device, and a projector disclosed in Japanese Patent Application Publication No. 2006-251459, an optical engine and an image projector including an optical engine disclosed in Japanese Patent Application Publication No. 2006-106683, a projector and an illumination optical system disclosed in Japanese Patent Application Publication No. 2004-286946, and the like.
However, there may be problems of light utilization efficiency and miniaturization in the optical device, image modulating device, and projector disclosed in Japanese Patent Application Publication No. 2006-251459 and the optical engine and image projector including an optical engine disclosed in Japanese Patent Application Publication No. 2006-106683.
Specifically, in regard to the problem of light utilization efficiency in the optical device, image modulating device, and projector disclosed in Japanese Patent Application Publication No. 2006-251459, there may be provided a light loss at the second surface of a prism which is a surface transmitting illumination light emitted from an exit aperture of light-guiding means and reflecting modulated light containing at least display light, and a light loss caused by diffusion of light, from an optical rod composed of a parallel rod part arranged at the side of the exit aperture and having reflection surfaces extending in a certain direction and a taper rod part arranged at an entrance aperture and extending such that the cross-sectional shape of its reflection surface is enlarged in a direction orthogonal to that extending from the side of the entrance aperture to the side of the parallel rod part, to a reflection-type image modulating device that is a DMD.
Furthermore, in regard to the problem of light utilization efficiency in the optical engine and image projector including the optical engine disclosed in Japanese Patent Application Publication No. 2006-106683, a light loss at surfaces on which a first prism adjacent to a condenser lens is applied and provided to a second prism adjacent to a DMD may be considered.
Herein, display light modulated by the DMD is reflected from the second surface of the prism and display light emitted from the prism which is light reflected from the second surface of the prism is projected onto a screen in the background art disclosed in Japanese Patent Application Publication No. 2006-251459. When the direction in which the display light modulated by the DMD is reflected from the second surface of the prism is the horizontal direction, the second surface of the prism extends in the vertical direction.
Furthermore, light rays reflected from the DMD are reflected from the surfaces on which the first prism adjacent to the condenser lens is applied and provided to the second prism adjacent to the DMD and an image is provided onto a projection surface by the light rays reflected from the surfaces on which the first prism is applied and provided to the second prism, in the background art disclosed in Japanese Patent Application Publication No. 2006-106683. When the direction in which the light rays reflected from the DVD are reflected from the surfaces on which the first prism is applied and provided to the second prism is the horizontal direction, the surfaces on which the first prism is applied and provided to the second prism extend in the vertical direction.
Meanwhile, the deflection angle of a movable micro-mirror of a DMD (digital micro-mirror device) is ±12°. In order to separate light reflected from the DMD from light incident on the DMD without an overlap between a light beam of the light incident on the DMD and a light beam of the light reflected from the DMD, the half cone angle of a light beam of any of the light incident on the DMD and light reflected from the DMD is 12° or less. Therefore, in order to maximize the light quantity of the light reflected from the DMD, the half cone angle of a light beam of any of the light incident on the DMD and light reflected from the DMD is a separation limit angle of 12° which is equal to the deflection angle of a movable micro-mirror.
Then, when such a light beam of the light reflected from the DVD which has a half cone angle of 12° is reflected from the second surface of the prism in the background art disclosed in Japanese Patent Application Publication No. 2006-251459 or reflected from the surfaces on which the first prism is applied and provided on the second prism in the background art disclosed in Japanese Patent Application Publication No. 2006-106683, it may be necessary for the critical angle of the second surface of the prism or the surfaces on which the first prism is applied and provided to the second prism to be 12°.
Herein, if the directions of the deflection of a movable micro-mirror of the DMD are the horizontal directions, the light reflected from the DMD is separated from the light incident on the DMD, and it may be possible to use a lens with F2.4 for projection optical means in Japanese Patent Application Publication No. 2006-251459 or a projection lens part in Japanese Patent Application Publication No. 2006-106683 in order to project a light beam of the light reflected from the DMD which has a half cone angle of 12°.
However, a movable micro-mirror of a DMD is deflected around an axis in the direction inclined by 45° with respect to the horizontal direction or vertical direction. Therefore, most of a light beam of the light reflected from the DMD overlaps with a light beam of the light incident on the DMD in the vertical direction and it may be difficult to well separate the light beam of the light reflected from the DMD from the light beam of the light incident on the DMD. Furthermore, because the light incident on the DMD is also incident on the DMD from the direction inclined with respect to the horizontal direction and the vertical direction, it may be difficult to well reflect a light beam of the light reflected from the DMD on the second surface of the prism in Japanese Patent Application Publication No. 2006-251459 or the surfaces on which the first prism is applied and provided to the second prism in Japanese Patent Application Publication No. 2006-106683, depending on the deflection of a movable micro-mirror of the DMD. Thus, a light loss may occur on the second surface of the prism in Japanese Patent Application Publication No. 2006-251459 or the surfaces on which the first prism is applied and provided to the second prism in Japanese Patent Application Publication No. 2006-106683 and about 40% of a light beam of the light reflected from the DMD which has a half cone angle of 12° may be lost.
In order to reflect a light beam having a circular cross-section shape on the second surface of the prism or the surfaces on which the first prism is applied and provided to the second prism, it may only be possible to reflect a light beam (with about F4.8 or greater) having a half cone angle of about 6° or less.
Thus, because light reflected from the second surface of the prism is projected in the background art disclosed in Japanese Patent Application Publication No. 2006-251459 or because light rays reflected from the surfaces on which the first prism is applied and provided to the second prism are projected in the background art disclosed in Japanese Patent Application Publication No. 2006-106683, a loss of a light beam of the light reflected from the DMD may occur on the second surface of the prism or the surfaces on which the first prism is applied and provided to the second prism.
Furthermore, there may be a light loss caused by diffusion of light from an optical rod composed of a parallel rod part arranged at the side of an exit aperture and having a reflection surface extending in a certain direction and a taper rod part arranged at the side of an entrance aperture and extending such that the cross-sectional shape of a reflection surface is enlarged in the direction orthogonal to extending from the side of the entrance aperture to the side of the parallel rod part, to a reflection-type image modulating device that is a DMD in the background art disclosed in Japanese Patent Application Publication No. 2006-251459, as described above.
When all of a light beam having a half cone angle of 12° is intended to be incident on a DMD, the size of the exit surface of the taper rod part at the side of the parallel rod part is (the length of one side of the effective area of the DMD)+2×(the distance from the exit surface of the taper rod part to the DMD)×tan (12°) and may be considerably greater than the length of one side of the effective area of the DMD. On the other hand, light emitted from the exit surface of the taper rod part diffuses at a certain angle. Herein, a loss of light which may be caused by its diffusion from the exit surface of the taper rod part to the DMD depends on the diffusion angle of light diffusing from the exit surface of the taper rod part or the distance from the exit surface of the taper rod part to the DMD. Because the parallel rod part is present between the taper rod part and the DMD in the background art disclosed in Japanese Patent Application Publication No. 2006-251459, a portion of light diffused from the exit surface of the taper rod part may diffuse to the outside of the parallel rod part. As a result, a light loss due to diffusion of light from the exit surface of the taper rod part may occur. Furthermore, a difference between the illuminance at a central portion of the effective area of the DMD and the illuminance at a peripheral portion of the effective area of the DMD or the difference between the illuminances at peripheral portions of the effective area of the DMD may be generated.
Next, there may be a problem of miniaturization in the background art disclosed in Japanese Patent Application Publication No. 2006-251459. As described above, when all of a light beam having a half cone angle of 12° is intended to be incident on a DMD, the size of the exit surface of the taper rod part at the side of the parallel rod part may be considerably greater than the length of one side of the effective area of the DMD. Therefore, it may be necessary to increase the size of the optical rod having the taper rod part.
Furthermore, there may also be a problem of miniaturization in the background art disclosed in Japanese Patent Application Publication No. 2006-106683. Because the optical engine includes a concave mirror and a condenser lens in addition to a prism module in the background art disclosed in Japanese Patent Application Publication No. 2006-106683, the size of the optical engine may increase.
Next, there may be a problem of light utilization efficiency, a problem of miniaturization, and a problem of complexity in the projector and illumination optical system disclosed in Japanese Patent Application Publication No. 2004-286946.
In the background art disclosed in Japanese Patent Application Publication No. 2004-286946, an integrator optical system for making uniform the intensity distribution of illumination light from a light source and emitting it is used. Herein, light emitted from the exit surface of the integrator optical system diffuses at a certain angle. In the background art disclosed in Japanese Patent Application Publication No. 2004-286946, a loss of light caused by its diffusion from the exit surface of the integrator optical system to a reflection-type modulation panel depends on the diffusion angle of light diffusing from the exit surface of the integrator optical system or its distance to a relay lens which generally conjugates the exit surface of the integrator optical system with the reflection-type modulation panel. That is, in other words, it depends on the diffusion angle of light diffusing from the exit surface of the integrator optical system and a finite effective diameter of the relay lens. Herein, a portion of light diffusing from the exit surface of the integrator optical system may diffuse to the outside of the finite effective diameter of the relay lens. As a result, a light loss caused by diffusion of light from the exit surface of the integrator optical system may occur. Furthermore, a difference between the illuminance at a central portion of the effective area of the reflection-type modulation panel and the illuminance at a peripheral portion of the effective area of the reflection-type modulation panel or a difference between peripheral portions of the effective area of the reflection-type modulation panel may be generated.
Moreover, the background art disclosed in Japanese Patent Application Publication No. 2004-286946 discloses a configuration such that a condenser mirror reflects illumination light from the relay lens which has transmitted through the inside of a prism, so as to transmit it through the inside of the prism again and a TIR surface of the prism totally reflects the illumination light from the relay lens so as to guide it to the condenser mirror, totally reflects the illumination light from the condenser mirror so as to guide it to the reflection-type modulation panel, and transmits a visual image light from the reflection-type modulation panel so as to guide it to a projection optical system, wherein the prism also reflects the illumination light from its surface other than the TIR surface and has at least five light paths in which the illumination light travels from a surface to a surface of the prism and inside the prism and passes through those light paths sequentially. That is, because the background art disclosed in Japanese Patent Application Publication No. 2004-286946 has at least five light paths in which the illumination light travels from a surface to a surface of the prism and inside the prism, the light paths of the illumination light are totally complicated and long. In particular, because the TIR surface of the prism totally reflects the illumination light from the relay lens so as to guide it to the condenser mirror and totally reflects the illumination light from the condenser mirror so as to guide it to the reflection-type modulation panel, it may be inevitable that the size of the prism will be increased in order to totally reflect all of an effective light beam of the illumination light twice.
Furthermore, because it may be necessary to arrange the condenser mirror close to a surface of the prism or to provide a prism surface which is a curved surface and provide the curved surface with a reflective coating such that it is a condenser mirror in the background art disclosed in Japanese Patent Application Publication No. 2004-286946, the configuration of the prism may be complicated and the prism may be expensive.